Project Summary: The Pitx2 homeodomain transcription factor is a central transcriptional regulator in left right asymmetry that functions within the heart to control cardiac morphogenesis. It is now clear that Pitx2 is fundamentally connected to AF although the basis for this connection remains obscure. The first evidence for the Pitx2-AF link was made in a Genome Wide Association Study (GWAS) implicating a region of chromosome 4q25 in early onset familial AF. Pitx2 was the gene in closest proximity to the disease associated single nucleotide polymorphism (SNP). AF patients with the 4q25 SNP were free of hypertension, diabetes and valve defects. Moreover, patients with the 4q25 SNP were more prone to cardioembolic stroke adding further urgency to gain insight to the underlying molecular mechanisms associated with the 4q25 SNP. We were the first group to report that Pitx2 heterozygous mice were predisposed to AF indicating that reduced levels of Pitx2 led to AF. Three different groups have subsequently replicated our findings. Because of its critical role in AF, we hypothesized that genome wide analysis of Pitx2 transcriptional target genes would provide novel and fundamentally important insight into the molecular mechanisms for AF in the Pitx2 happloinsufficient state. Our preliminary Chromatin Immuno Precipitation (ChIP) sequence (seq) data indicate that Pitx2 directly binds to a number of genes that have been implicated in AF and also genes that respond to reactive oxygen species. Moreover, our preliminary data indicate that Pitx2 may be regulate by the Hippo pathway, an essential cardiac regenerative pathway. There is poor understanding of the genetic mechanisms underlying AF. New genetic insights will be critical for diagnostic testing and family counseling in the future. Moreover, an in depth knowledge of genetics of AF will provide critical resources for patient management as human genome sequencing becomes more commonplace. Finally, there is the long term goal to develop novel therapeutic strategies based on solid scientific information that will come from work in model organisms and human genetics.